1. Field of the Invention
This invention relates to synthesizing an expressive portamento transition between musical tones and controlling this portamento transition by modifying the effect of a pitch wheel control signal. In particular, the present invention pertains to synthesizers capable of responding to a typical pitch wheel control by generating slide-step-slide and slide-step portamento pitch curves
2. Background Art
An important part of the expressive control exercised by a wind or string player involves controlling precisely how pitch changes from note to note and, in particular, how pitch changes during the transition from one note to the next. For example, when a violinist plays two notes of different pitches in succession he may choose to change the pitch in an abrupt manner or he may slide from the first pitch to the second by sliding his finger along the fingerboard in a continuous manner. This is called portamento. If the violinist slides from note to note-on the same string without changing the bow then the portamento pitch curve is very smooth with no discernable discontinuity in pitch from the first pitch to the second as shown in FIG. 1 (Background Art).
However, the violinist may also change bow direction at some point during the slide, the violinist may change the finger that depresses the string during the slide, or the violinist may change which string is bowed during the slide. In these later cases there is typically a more complex pitch curve. FIG. 2 (Background Art) shows a graph of pitch against time during a violin portamento of this type where the pitch of the first note is C and the pitch of the second note is G. As can be seen, towards the end of the first note the pitch begins a gradual slide away from C and toward G. At the beginning of the second note the pitch steps abruptly to a value somewhat below G. Then the pitch slides finally reaching G. This shape consisting of slide-step-slide is typical of many violin portamentos. Controlling the rates and amounts of the slides, the size of the pitch step, and the character of the articulation when the pitch step occurs is central to expressive violin playing. Other string instruments—viola, cello, contrabass—behave similarly to the violin. Wind instruments may employ a similar expressive control over portamento but to a lesser extent.
Another portamento variant is shown in the complex pitch curve of FIG. 3 (Background Art). This is the same as FIG. 2 except that the final slide is omitted. Instead at the beginning of the second note the pitch jumps all the way to G. This is the slide-step pitch curve.
A typical electronic musical synthesizer such as a MIDI keyboard instrument includes a piano or organ-like keyboard and a pitch wheel control. The pitch wheel control has a center detent position. Using one hand a performer can displace the pitch wheel control in a continuous manner above or below the center detent position. If the performer releases the pitch wheel it automatically returns to the center detent position.
When a note is struck on the keyboard a musical tone begins. In the typical musical synthesizer, at any instant the exact pitch of the musical tone is related to the sum of the pitch indicated by the struck key on the keyboard—C, D, F# etc—and the position of the pitch wheel. The pitch wheel enables the performer to “bend” the pitch in a quasi-continuous manner above or below the pitch indicated by the struck key.
A typical music synthesizer may also include a separate portamento control. When two notes of different pitches are played on the keyboard in succession, the portamento control determines the shape of the pitch change. With portamento set to zero, when the second note is played the pitch changes abruptly to the pitch of the second note. With non-zero portamento values, when the second note is played the pitch begins a gradual slide from the first note pitch to the second note pitch. The exact non-zero portamento value determines the rate of change of the pitch during this slide.
Suppose the performer wants to generate a slide-step-slide portamento transition as described above using the standard pitch wheel. Further, suppose that the performer is playing in a reasonably legato fashion so that the first note-off occurs either after the second note, at the second note-on, or very shortly before the second note-on. If the first note-off is at or after the second note-on then the sound continues without interruption between the first and second notes. If the note-off occurs slightly before the second note-on we assume that the note takes a finite amount of time to die away—e.g. 0.05 seconds—so that again the sound is substantially continuous from the first to the second note.
The performer can effectively perform the initial pitch-slide that occurs at the end of the first note. However if the performer continues to hold the pitch wheel after the second note is struck the pitch jumps to the keyboard pitch plus the current value of the pitch wheel. If the performer quickly releases the pitch wheel after striking the second note an undesirable quick slide back to the target pitch occurs. This is shown in FIG. 4 (Prior Art) where the additional dotted line curve at the bottom of the graph shows the motion of the pitch wheel beginning at its initial zero value center detent position.
Alternatively, if the performer releases the pitch wheel just prior to striking the second note there is an equally undesirable bend back to the first pitch before jumping abruptly to the second pitch. This is shown in FIG. 5 (Prior Art). It is almost impossible to synchronize the pitch wheel motion with the note starts in a manner that avoids the above two problems. As a result it is nearly impossible to achieve the desired slide-step-slide or slide-step pitch curve using the standard pitch wheel.
The portamento-control also does not support the generation of slide-step-slide pitch curves. The pitch shapes are deficient in two ways: first, the pitch slide does not begin until the second note is played on the keyboard; second, the pitch slides continuously from the first note pitch to the second note pitch—there is no step. This is shown in FIG. 6 (Prior Art).
Both MIDI portamento control and standard MIDI pitch wheel curves have shortcomings. A need remains in the art for apparatus and methods for generating portamento transitions in synthesized music which better model portamento transitions in musical performances.